Generally, a liquid crystal display (LCD) device includes a first substrate having a first electrode, a second substrate having a second electrode opposite to the first electrode, and liquid crystal disposed between the first and second substrates. The liquid crystal display device changes an alignment of liquid crystal by applying electric field to both the first and second electrodes to adjust quantity of light passing through liquid crystal, thereby displaying various images.
Twisted nematic (hereinafter, referred to TN) liquid crystal, in which a long axis of liquid crystal is continuously twisted from the first electrode towards the second electrode at a right angle, is mainly used in the liquid crystal display device.
Although TN liquid crystal is irregularly aligned, it has a predetermined alignment order with respect to an axis of liquid crystal. TN liquid crystal has different physical properties in a long axis direction and a short axis direction thereof, respectively. That is, TN liquid crystal has optically anisotropic characteristic.
Hereinafter, a conventional TN-type liquid crystal display device, which displays images by using above-mentioned TN liquid crystal, will be described.
FIG. 1 is an exploded perspective view of a conventional TN-type liquid crystal display device 400.
Referring to FIG. 1, the TN-type liquid crystal display device 400 includes a backlight unit 200 for generating light, a display unit 100 for receiving light from the backlight unit 200 to display images, a mold frame 250 for accommodating the backlight unit 200 and the display unit 100, and a chassis 300 therein.
The display unit 100 has a liquid crystal display panel 110 for displaying images, printed circuit boards 120 and 140 for supplying a driving signal and an image data signal to the liquid crystal display panel 110, and tape carrier packages (hereinafter, referred to TCP) 130 and 150 disposed between the liquid crystal display panel 110 and the printed circuit boards 120 and 140 in order to electrically connect the printed circuit boards 120 and 140 to the liquid crystal display panel 110.
The liquid crystal display panel 110 includes a thin film transistor substrate (hereinafter, referred to TFT substrate) 112 having thin film transistors (TFTs, not shown) and pixel electrodes (not shown), a color filter substrate 114 opposite to the TFT substrate 112 and having color filters and common electrode, and liquid crystal (not shown) disposed between the TFT substrate 112 and the color filter substrate 114.
In detail, the TFT substrate 112 includes a plurality of data lines (not shown) extended in a row direction thereof and a plurality of gate lines (not shown) extended in a column direction thereof. In addition, a plurality of TFTs are arranged on the TFT substrate 112 in a matrix shape. That is, source electrodes of the TFTs are connected to the data lines, and gate electrodes of the TFTs are connected to the gate lines. Drain electrodes of the TFTs are connected to the pixel electrodes.
One end of each data line is coupled to a data-side TCP 130 equipped with a data driver chip, and one end of each gate line is coupled to the gate-side TCP 150 equipped with a gate driver chip.
The data-side TCP 130 is connected to a data-side printed circuit board 120 so as to timely apply image data signal inputted from the data-side printed circuit board 120 to the data lines. In addition, the gate-side TCP 150 is connected to the gate-side printed circuit board 140 so as to apply a gate driving signal inputted from the gate-side printed circuit board 140 to the gate lines.
On the other hand, the backlight unit 200 includes a light source 210 for generating first light, and a light guiding plate 220 for guiding the first light towards the liquid crystal display panel 110. The light source 210 includes a lamp (lamps) 211 generating the first light and a lamp reflection plate 213 covering one side of the lamp (lamps) 211 to reflect the first light towards the light guiding plate 220.
The light guiding plate 220 is disposed at the other side of the lamp 211 and includes an incident surface through which the first light is incident, a reflection surface for guiding the first light towards the liquid crystal display panel 110, and an exiting surface for outputting the first light towards the liquid crystal display panel 110.
In addition, the backlight unit 200 includes a reflection plate 240 and a plurality of optical films 230. The reflection plate 240 is disposed below the light guiding plate 220 and reflects light leaked from the light guiding plate 220 towards the liquid crystal display panel 110. The plurality of optical films 230 allows the light outputted from the light guiding plate 220 to have uniformly distributed luminance.
Since the conventional TN type liquid crystal display device 400 having the above structure uses the TN crystal having optical-anisotropic characteristic, a color and a contrast ratio (C/R) of the images vary depending on viewing angles. Therefore, the conventional TN type liquid crystal display device 400 may limit a range of viewing angles for allowing a user to precisely recognize information displayed in a screen of the conventional TN type liquid crystal display device 400.
Although it is not shown in the figures, the conventional liquid crystal display device includes a compensating film (wide view film) having a discotic layer so as to solve the above problem. However, although the compensating film can improve the viewing angle, gray scale inversion occurs when the viewing angle exceeds a predetermined level.
That is, a normal gray level can be found when a user look at the liquid crystal display panel 110 at a front thereof However, an abnormal gray level is found when a viewing position of the user is changed upward or downward the front of the liquid crystal display panel 110. When the liquid crystal display panel 110 is viewed with a viewing angle exceeding a critical viewing angle, a white gray scale is erroneously recognized as a black gray scale, or the black gray scale is erroneously recognized as the while gray scale, called “gray scale inversion”.